Lathe for engraving cylindrical surfaces, with self-rectification



T 2,578,222 NDRICAL SURFACES TIFICATION so, 1945 Dec. 11, 1951 BON LATHE FOR ENG ING CY WITH SELF- Filed O Patented Dec. 11 1951 UNITED STATES PATENT OFFICE LATHE FOR ENGRAVING CYLINDRICAL SURFACES, WITH SELF-RECTIFICATION Maurice Bonnet, Paris, France, assignor to La- Reliephographie, Societe pour lExploitation des Procedes de Photographic en Relief Maurice Bonnet, Paris, France, a French corporation Application October 30, 1945,:S'erial No. 625,605

In France June 25, 1941 Section 1, Public Law 690 August 8, 1946 Patent expires J une 25, 1961 2 Claims. 1

The present invention has for its subject-matter a lathe for engraving cylindrical surfaces for the purpose for example, of producing optical selector nets with lenticular elements by a subsequent goffering operation.

In a lathe of this character a tool engraves on a rotating cylinder a helicoidal groove having a concavity corresponding with the curvature of the lenticular elements of the net. Owing to the size of the groove, which varies between a few tenths and a few hundredths of a millimeter, it is necessary for the lathe to be of very accurate construction, whilst the means which are generally used are not capable of ensuring the necessary stability for the purpose.

Therefore, the invention relates to a plurality of" means which render it possible as a result of their combination, to obtain a degree of stability and accuracy hitherto not obtainable.

According to the invention, the reciprocal movement of translation between the tool and the cylinder is no longer obtained by a longitudinal movement of the toolholder along a bench, but by the movement of the cylinder itself and of the shaft by which it is carried, the tool remaining stationary once it has been adjusted. It has been found that the transmissions of movement to the usual lead-screws and the devices for guiding the tool-holder along a straight line on the bench constitute an unstable unit which always sets up friction, vibrations and disturbances to which the engraving is subjected to an inadmissible extent. In the present invention, the weight of the movable unit is, without doubt, greater, but its mass constitutes per se a factor of stability. Further, as the shaft which carries the cylinder rotates at the same time as it is moved longitudinally, the force necessary for producing its movement is considerably reduced. Also, the parts used for guiding the shaft dur-, ing its longitudinal movement are the same as those used for guiding it during rotation, whereby the whole construction is simplified.

According to another feature of the invention, the longitudinal movement of the cylinder and of its shaft is produced by means of a screw, secured to the end of the latter, which is rotated by the shaft itself through the medium of a driving device having a great fredom of movement and applying a thrust to the shaft through the medium of an axial ball or point whereby the cylinder is prevented from carrying out a movement which may be caused by any possible lack of alignment between the shaft and the screw or any eccentricity of the later which is.

entirely free to move between its point of securing to the shaft and its supporting point formed by the nut which it engages, so as to avoid any risk of jamming.

According to the invention, the screw is made of a metal which is softer than that of the nut, the latter being of a type allowing the back lash to be taken up. Thus, any possible wear of the thread is distributed uniformly throughout the length of the screw instead of affecting only the threads of the nut, whilst the latter, acting as a screw die, continually rectifies the screw, thus ensuring an always constant feed of the shaft and of the cylinder.

The same means of automatic rectification is provided for the shaft in its bearings which are also of a type allowing the back-lash to be taken up.

Further, all the bearings and the nut are mounted in staysmoving about two axes of rotation perpendicular to one another in order to allow of satisfactory alignment thereof during the mounting, whereupon the bearings and the nut are locked in their final position.

The longitudinal movement of the shaft is facilitated by a axial traction device provided with a counter-weight, said device relieving the screw from the greater part of its thrust (which is already reduced as a result of the rotation of the shaft), so as to cause it to operate as a measuring member instead of as a driving part, which is of advantage as regards its life and its accuracy.

Another feature of the invention consists in the fact that the shaft is rotated at its end re mote from the screw by a slidably keyed sleeve provided with means preventing any jamming.

In order to obviate any tendency to rise of upward movement which is liableto be caused by reaction of the tool on the cylinder by the pres ence of a chip, bushes are provided in the lower part thereof with a recess so that they act somewhat as a centering V-piece ensuring an accurate bearing of the shaft under the action of gravity on the remainder of the lower part of the bushes.

Finally means are provided for obtaining considerable accuracy while preventing play direction, these means consisting in inclining the whole unit of the machine relatively to its 1ongitudinal axis at an angle which still ensures a sufficient bearing surface for the shaft in its notched bushes.

In. the accompanying drawings:

Figure 1 is a diagrammatic view partly in ele- 3 vati'on and partly in section of a lathe according to the invention.

Figure 2 is a section on the line A-B of Fig? ure 1 to. a larger scale showing means for guiding a shaft in a driving sleeve.

Figure 3 is a partial plan of the central portion of Figure 1.

Figure 4 shows One of the bushes of the lathe i to a larger scale.

A frame I is provided with bearings 2 in each of which is supported a stay 3 journalled in the bearing 2 by means of a stud 4. Bushes 5 are journalled in the stays 3 by means of the studs 6 which are perpendicular to the studs 4. The studs 4 and 6 may be locked in the bushes 5 after alignment, by any suitable means, not shown. The bushes 5 are of any type which allow the backlash to be taken up and comprise for example, a threaded cone on which a clamping ring is threaded.

The frame I also supports a tool-holder block I in which a tool 8 is mounted so a to be adjustable in all directions by any usual means.

On a shaft 9 is mounted a cylinder Hill around which is stretched a copper sheet which is to receive an engraving, said cylinder I80, as shown, being located between tWo stays 3. The copper sheet may be bent around the cylinder and secured in a usual manner. If the sheet is cylindrical, the shaft 5: may be removed from its supports sleeve I I which is rotated for example by a pulley I2 rigidly secured thereto.

The shaft 9 is driven by the sleeve I I by means of five ball bearings I3, it, I5, It, IT. The bearings l3, I4 and I? engage with the three free faces of the rib It, whilst the bearings I5 and i6 engage directly with the shaft 9. By reason of this arrangement any liability of the shaft 9 becoming wedged in ide the sleeve I 9, Whilst being rotated by the sleeve II, is obviated.

A traction device including a counter-weight I8 acts on the left hand end of the shaft 9: the mass of the counter-weight I8 being so selected that it is almost capable of producing axial movement of the shaft 9 and of the cylinder mi secured to the latter when the shaft 9 and the cylinder I60, 5

separated from a screw 23, rotate at their normal speed.

At its other end, the shaft 9 carries a flange I9 provided in its centre with a recess fora ball 20. The flange I9 also carries at its periphery driving members 2 I, for example, pins, by which a fiange 22, secured to the screw 23 is rotated. The driving members 2i shown as pins in openings in the flange 22 will hold the parts I9 and 22 together and in some cases, positive connecting elements such as studs, bolts and similar devices may be used. The flange 22 is also provided with an axial recess for the ball 23. At its right hand end, the screw 23 engages with a nut 25 which is also of a type enabling back-lash tobe taken up.

As shown in Figure 4, the bushes 5 are provided with cut out portions 25 one of which is provided in the lower part of each bush 5.

The bushes 5 and the nut 24 are made of a metal which i harder than the metal or metals of which the shaft 9 and the screw 23 are made.

The operation of the engraving lathe which forms the subject matter of the present invention is as follows:

, Figure 1 shows in full lines the position of the parts at the end of an engraving stroke, the start ing position being indicated by chain-dotted lines. When the tool 8 has been suitably adjusted relatively to the cylinder IUD, when this occupies its starting position, the shaft 9 is rotated through the medium of the sleeve II, the ball bearings I3--I'I and the key Ill. At the same time the crew 23 is rotated by the members EI and accordingly moves towards the left of the drawing as a result of its engagement with the nut 24. The screw 23 transmits its axial thrust to the shaft 9, which slides in the bushes 5 and in the sleeve I I, through the ball 20, the bearings l3--Il rotating during this movement.

As a result of the combined rotary and longitudinal movement of the shaft 9, the tool 8 cuts in the cylinder I90 a groove of which the shape is determined by the tool 8 and the pitch by the pitch of the screw 23 in the example shown.

By the action of the counter-weight I8 the thrust exerted on the shaft 9 by the screw is reduced to a minimum.

It is also to be observed that during the operation of the lathe the sections of the shaft 9 and of the screw 23 which are supported in the bushes 5 and in the nut 2 are of different cross sectional area, so that by reason of the difference of hardness of the metals used, a continuous rectification of the shaft and of the screw is obtained at the expense of negligible wear which, moreover, can be compensated easily by means of the devices for taking up the back-lash in the bushings and the nut.

In spite of the action of the counter-weight I8, the thrust applied by the screw 23 would not be consistent with a regular operation of the lathe unless the shaft rotated at the same time as it moved axially; however a combination of these two movements makes it possible to move it longitudinally by a very small thrust.

It will be understood that the lathe has been shown only very diagrammatically in the drawings and Without specific proportions. Numerous constructional modifications may be made in the various parts without departing from the scope and spirit of the invention. Such modifications are necessary, for example, when the lathe is inclined as a whole longitudinally, as above described, in which case the counter-weight traction device may, of course, be omitted.

According to the invention, it is also possible to interpose a speed reducing gear, including pinions, between the shaft and the screw, the latter, however, always acting, axially upon the shaft, in order to obtain for the cylinder a feed equivalent only to a fraction of the pitch of the screw.

In a general manner, all the elements of the lathe are large sized and have a considerable weight, this being beneficial to the stability and the inertia of the whole.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

l. A lathe for engraving cylindrical surfaces comprising a stationary tool-holder, a tool carried thereby, a work-carrying shaft, two stationary bearings, directly supporting the shaft, means engaging one end of said shaft and adapted to ,give it a rotary movement, means der adap ted to receive the surface to be engraved,

5 and rigidly carried by said shaft in front of the tool holder between the two bearings, axially spaced apart a distance only sufficient to enable axial translation of the shaft and cylinder carried thereby.

2. A lathe for engraving cylindrical surfaces comprising a stationary tool holder, a tool carried thereby, a work-carrying shaft, means for imparting to said shaft a longitudinal movement parallel to its axis, a longitudinal rib projecting above the surface of the shaft and, the length of which is at least equal to the maximum path of the shaft in its longitudinal motion, ball bearings engaging the sides and outer face of the rib and spaced portions of the shaft opposite said rib, a longitudinally stationary driving sleeve slidingly fitted over the shaft and adapted to act through said bearings on the shaft and on the rib, for causing said shaft to rotate, means for imparting a rotary movement to said sleeve, and a cylinder adapted to receive the surface to be engraved and carried rigidly by said shaft between two bearings in front of the toool holder.

MAURICE BONNET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,159,739 Bock Nov. 9, 1915 1,238,934 Olson Sept. 4, 1917 1,339,836 Vernon May 11, 1920 1,445,137 Harris Feb. 13, 1923 1,503,320 Hardel July 29, 1924 1,753,384 Merritt Apr. 8, 1930 1,955,658 Roddel Apr. 17, 1934 2,250,369 Gorton July 22, 1941 FOREIGN PATENTS Number Country Date 453,843 Germany Dec. 21, 1927 

